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Distribution of Krakow’s Population by Dasymetric Modeling Method Using Urban Atlas and Publicly Available Statistical Data

Pirowski T, Pomietłowska J.

Geomatics and Environmental Engineering

2017

Vol. 11, no. 4

83--95

Tematem publikacji jest zaadaptowanie dazymetrycznej metody mapowania powierzchni statystycznej do badania gęstości zaludnienia oraz skartowania rozmieszczenia ludności Krakowa. Opracowania ludnościowe dla miast są ważne w aspekcie planowania przestrzennego i urbanistycznego oraz sporządzania analiz rynkowych bądź kryzysowych. Dotychczasowe mapy ludności Krakowa sprowadzają się do kartogramów prostych odniesionych do jednostek podziału administracyjnego. Bazując na podejściach podanych w źródłach literaturowych oraz odpowiednio je modyfikując z uwzględnieniem charakteru i szczegółowości posiadanych danych, opracowano trzy mapy rozmieszczenia ludności Krakowa: metodą binarną oraz, w dwóch wariantach, metodę powierzchniowo-wagowej agregacji. Jako zmienne ograniczające wykorzystano dane o pokryciu i użytkowaniu terenu Urban Atlas z 2009 roku, dostępne w ramach programu GMES Urban Audit. Dane statystyczne o ludności poddane przeliczeniu pochodziły z 2009 roku i były opracowane dla 141 jednostek urbanistycznych Krakowa. Przyjęte arbitralnie wartości dotyczące liczby ludności, przypisane poszczególnym typom pokrycia terenu (dwa pierwsze realizowane podejścia), upraszczają przeliczenie ludności miasta, gdyż zakładają możliwość skutecznego przeniesienia wprost doświadczeń z innych obszarów testowych. W rozwiązaniu trzecim zoptymalizowano więc metodę powierzchniowo-wagowej agregacji, uzyskując nowe proporcje w zagęszczeniu ludności dla wydzielonych charakterystycznych kategorii pokrycia terenu na obszarze Krakowa. Analizując dla poszczególnych trzech testowanych rozwiązań kartogramy błędów oraz ich rozkład na histogramach, potwierdzono zasadność takiego podejścia. Uzyskana mapa stanowi lepsze odzwierciedlenie rzeczywistego zróżnicowania przestrzennego ludności Krakowa niż stosowane dotychczas kartogramy proste czy modelowanie dazymetryczne nieuwzględniające specyfiki kartowanego obszaru.

This publication attempts to adapt the dasymetric method of mapping statistical areas to study population density and carry out the mapping of population distribution of the city of Krakow. Population studies of cities are an important issue, both from a spatial and urban planning point of view and in the preparation of market or crisis studies. Existing maps of the population of Krakow come down to simple cartograms referenced in administrative divisions. Based on the approaches given in literary sources (and modifying them appropriately with regard to the nature and detail of the data already in place), three population distribution maps of Krakow were developed using the binary method and – in two variable options – surface-weight aggregation. Data on land cover and use from the 2009 Urban Atlas was used as a limiting variable, available under the GMES Urban Audit program. The statistical data on population that required conversion from administrative units into built-up areas came from 2009 data developed for the 141 urban units of Krakow. Arbitrarily adopted numbers of people assigned to particular types of land cover (the first two implemented approaches) generalize the population distribution of the city and/or assume the possibility of a direct transfer of experience from other areas to the analyzed area. Therefore, in the third solution, an optimization of the surface-weight aggregation method was made, obtaining new characteristic proportions for Krakow in the population density for inhabited categories of land cover. When analyzing cartograms and histograms of errors noted within the urban units, the validity of this approach was confirmed. The map generated provides a better reflection of the actual spatial diversity of the population of Krakow than the previously used simple cartograms (or the dasymetric modeling, which did not take into account the specifics of the mapped area).

Modelowanie powierzchni statystycznej przedstawiającej gęstość zaludnienia w Polsce przy pomocy metody dozymetrycznej

Bielecka E., Kuczyk A., Witkowska E.

Roczniki Geomatyki

2005

T. 3, z. 2

10-16

Population mapping, in general, has two purposes: firstly, to cartographically portray the extent and density of population across an area of interest, and secondly, to derive a quantitative estimation of population density for use in subsequent spatial analytical modeling tasks. A cartographic portrayal of population traditionally has the form of a choropleth map. This kind of mapping is very simple, but despite its simplicity, choropleths maps have limited utility for detailed spatial analysis of population data, especially where human populations are concentrated in relatively small numbers of villages, towns and cities. One way to avoid this limitation is to transform the administrative units into smaller and more relevant map units through the process known as dasymetric mapping. The dasymetric technique maps a quantitative variable according to boundaries derived from the character of the data distribution. It is a form of an areal interpolation that uses ancillary data to transform population data from one set of spatial units to another. This paper demonstrates the use of satellite derived ancillary land cover data to map population densities using dasymetric mapping. The three dasymetric methods presented, revealed the interregional variation in population density more realistically, in particular, among urban and rural areas. The methods were tested for Mazovia Region. The binary method, the simplest, is easy to implement in GIS and gives a better view of population distribution over a given area than conventional choropleth maps (fig. 1). The only drawback is the delimitation of uninhabited areas. The areal weighting aggregation method uses land cover data as limiting variable and a typology of communes as a correlation variable. We a priori assign the percentage of people attributed to each land cover type and groups of communes. Subjectivity of these decisions is considered the drawback of the method. The results are detailed enough and portray population density very realistic (fig.2). The areal weighting correlation method presents a new way of calculating weighting coefficients. This is based on the method proposed by Gallego and Peedell (2001), but is adapted to Polish conditions by grouping land cover classes, stratifying communes and computing coefficients (tab.1). This dasymetric mapping method is based on the assumption that the ratio between the population density of two land cover categories is the same for any given commune. This method, on contrary to previous ones, does not preserve pycnophylactic property of statistical data, so it is necessary to evaluate the results. Relative errors were computed for evaluating the modified areal weighting method. The analyse of a comparison between attributed population and population data known from statistical measurements indicate that the population value attributed to most of the communes is approximately in agrement with the statistical data (fig.4). The coefficients seem to be too high for a few urban communes and too low for some rural areas. The areal weighting correlation method provides realistic view of population distribution in the Mazovia Region (fig 3). The dasymetric population map was visualized according to choropleth map rules in such a way that it focuses on the relationship between settlement and the natural environment. The information generated from a dasymetric population density map could provide useful assistance to district administrations, especially those responsible for regional or city development and land management.